1. Field of the Invention
The invention relates to liquid crystal display (LCD) devices, and in particular to substrate structures for LCD devices and fabrication methods thereof.
2. Description of the Related Art
Liquid crystal display (LCD) devices have many advantages such as small volume, light weight and low power consumption, and due to liquid crystal displays feature lighter weight, thinner profile, and increased portability are applicable in a variety of electronic and communication devices including notebook computers, personal digital assistants (PDA), mobile phones and the like.
A silicon oxide (SiOx) layer is formed as an alignment layer in conventional optical compensated birefringence (OCB) mode LCD devices to improve viewing angle. The orientation of the silicon oxide (SiOx) layer is determined during deposition, thereby the pre-tilt angle of liquid crystal molecules is controlled to a range between 30-60 degrees. The silicon oxide (SiOx) layer, however, must be deposited in a vacuum, resulting in intricate fabrication procedures and reduced throughput.
Additionally, luminance of conventional transflective LCDs are different in transmission mode and reflection mode, leading to unsaturated images. The alignment layers in reflection and transmission regions are different to meet different pre-tilt requirements of the liquid crystal layer. For example, conventional addition of photo-catalyst in polyimide (PI) and selective exposure due to photo-chemical reaction can create different orientation alignment layers.
FIG. 1 is a schematic view of a conventional transflective LCD device with different orientation in the reflection and transmission regions. In FIG. 1, a transflective LCD comprises a lower substrate 11 such as an active device matrix substrate, an opposing upper substrate 12 with color filters 15 thereon, and a liquid crystal layer 13 interposed between the upper and lower substrates. The lower substrate 11 includes an active device array such as a thin film transistor (TFT) array on a transparent substrate. A display area of the lower substrate 11 can be divided into a reflection region R and a transmission region T. A transparent electrode 19 is formed on the lower substrate 11 and electrically connected to the thin film transistor (TFT) via a contact 20. A reflective electrode 18 is deposited on the transparent electrode 19 in the reflection region R. A vertically oriented alignment layer 21 and a horizontally oriented alignment layer 22 are respectively disposed in the reflection region R and transmission region T of the lower substrate 11. In conjunction with a horizontal oriented alignment 22 on the upper substrate 12, different optical characteristics in reflective region R and in transmission region R can thus be achieved in a transflective LCD device.
U.S. Pat. No. 6,862,058, the entirety of which is hereby incorporated by reference, discloses a transflective liquid crystal display with different alignment orientations in the reflection region and in the transmission region. Different alignment layers are separately formed in the reflection region and in the transmission region to improve viewing angle. Forming different alignment layers, however, requires intricate lithographic processes, leading to high production cost and low yield.
Japanese Patent No. 7-92 467, the entirety of which is hereby incorporated by reference, discloses a liquid crystal display device with wide viewing angle. In each pixel region, different alignment layers are formed by lithography and etching, leading to high production cost and low yield.